The invention disclosed and claimed herein generally pertains to a mixed system for mobile telecommunications, wherein a mobile station (MS) can operate and be connected with any one of two or more core networks included in the system. More particularly, the invention pertains to a method or procedure for determining which of the core networks a mobile station should camp on, that is, which mode the mobile station should select to operate in.
In certain mobile telecommunications networks, operators are starting to deploy 3G networks, in order to deliver new and innovative services to end-users. A 3G network could either be supplanted in existing 2G cells such as GSM/EDGE Radio Access Network (GERAN) or be deployed separately such as for UMTS Terrestrial Radio Network (UTRAN). The 2G networks will remain in place for legacy terminals so that both 2G and 3G will co-exist for many years to come. One aspect of this coexistence is seamlessness. The end-user while using multi-mode phones expects to be able to roam and stay connected while moving between these two networks.
Current 2G and 3G mobile networks are each separated into a radio access network (RAN) and a core network (CN). The RAN deals with radio resource handling while the CN provides other services such as mobility management, IP address allocation and call control facilities to the user equipment (UE). Core network services are provided in both the packet-switched and circuit-switched domains.
The control of which cell a mobile station (MS) should communicate with is controlled by the RAN and the MS. The RAN controls the cell selection in connected mode on dedicated channels and by admission control, while the MS controls the cell selection in idle mode and on shared channels in connected modes. As is known, an MS is in idle mode when it is roaming and switched on, in a non-active mode. The MS behavior in the MS controlled cases is standardized, and the algorithms and criteria for the Public Land Mobile Network (PLMN) and for cell selections are in accordance with the GSM and UTRAN standards.
However, with the introduction of cells such as GERAN that support both the 2G and 3G core networks, as well as mixed networks supporting different radio access technologies (RAT), an enhanced cell selection needs to be made available. The problem is that with the introduction of cells such as GERAN, a single GSM cell will now support both the 3G (Iu) and 2G (A/Gb) core network access. At the same time, there is currently no efficient way for the operator in a mixed system to control which of these core networks the MS should camp on, that is, which mode the MS should operate in. Potentially, this may cause the MS to bounce between two CN access nodes when moving between cells supporting 2G only and cells supporting both 2G and 3G core networks. This would lead to extensive location updating signaling in the mixed network. The RAN would have to transparently transport these messages, and the core network would actually have to process them. The information regarding the UE in the core network (PDP context) would actually bounce between the 2G and 3G Serving GPRS nodes. This is generally unacceptable behavior. Presently, no solutions for interface selection have been presented in any standard.
Herein, the terms “mixed system” and “mixed network” are used to refer to a telecommunications system having two or more core networks such as 2G and 3G.